1. Field of the Invention
The present invention relates to an opening apparatus for bags in which a nozzle is moved into mouths of respective bags that are continuously conveyed and a gas is jet into the bags from a discharge opening of the nozzle.
2. Prior Art
Continuous conveying type bag-filling packaging machines perform a series of packaging operations while self-standing bags are continuously conveyed. Such operations includes opening of the bag mouths, spreading of the bag bottoms by blowing a compressed gas into bags, filling of the bags with contents and sealing of the bag mouths.
Typical continuous conveying type bag-filling packaging machines include either one of two types of bag mouth opening apparatuses: a following-reciprocating motion type apparatus and a rotary loop type apparatus.
In the following-reciprocating motion type, a nozzle that blows a gas into the bags repeats a following motion and a return motion in the conveying direction of the bags. During the following motion, the nozzle is advanced toward the mouth of the corresponding bag and is inserted into mouth. Then, a gas is blown into the bag from the discharge opening of the nozzle, so that the bag bottom is spread open. The nozzle is next retreats and is separated from the bag mouth. However, this type has several problems.
First, a certain distance is required for the acceleration of the nozzle from a stopped state to a bag conveying speed, and a certain deceleration distance is also required in order to stop the nozzle after the nozzle is separated from the bag mouth. As a result, the distance required for the reciprocating motion of the nozzle tends to be correspondingly long, so that overall size of the packaging machine increases, requiring a large installation space.
Second, time is likewise required for acceleration and deceleration, and this hinders increase in the running speed of the packaging machine.
Third, since the reciprocating motion and advancing and retracting action of the nozzle are repeated, vibration and noise are considerable, deteriorating the working environment. This problem becomes more conspicuous as the packaging machine is operated at higher speeds.
Fourth, in cases where a plurality of sets of nozzles are installed and a plurality of bags are opened at one time, the inertia becomes large, thus requiring an additional distance and time for acceleration and deceleration, leading to an increase in the size of the apparatus, and making it difficult to achieve a desired speed increase.
In the rotary loop type, on the other hand, numerous nozzles are installed at equal intervals on a chain that is mounted on a pair of sprockets, and these nozzles are caused to revolve at the same speed as the conveying speed of the bags. A part of the revolving path of these nozzles is set to run along the conveying path of the bags; and in this area of revolving path of the nozzles, the nozzles are advanced toward the bag mouths and inserted thereinto. Then, a gas is jet into the bags from the discharge openings of the nozzles so as to spread the bottoms of the bags, after which the nozzles are retracted and separated from the bag mouths.
In this rotary type, however, the structure that causes the nozzles to revolve and to advance and retract is complicated. Furthermore, since the nozzles revolve in the horizontal plane, the connecting structure of the nozzles with a compressed gas source, etc. is also complicated, and the maintenance and cleaning characteristics are poor, thus being costly. In addition, since the structure is large in size, a large installation space is required for the packaging machine as whole. Moreover, the vibration and noise derived from the advancing and retracting action of the nozzles are present as in the above-described following-reciprocating motion type apparatus.
The present invention is to solve the problems with the prior art bag opening apparatuses used in continuous conveying type bag-filling packaging machines.
It is, therefore, an object of the present invention to provide an apparatus for opening bags that is simple in structure and compact in size, produces little vibration and noise and increases the speed of operation.
The above object is accomplished by a unique structure for an opening apparatus for bags in which a nozzle is inserted into a mouth of a bag among bags that are continuously conveyed at a constant speed and uniform intervals, and a gas is caused to jet into the bag from a discharge opening of the nozzle so as to open the bag, and in the present invention,
the nozzle is continuously revolved on a circular track with the discharge opening thereof being kept to face the bottom of the bag so that the discharge opening advances toward and withdraws from the mouth of the bag which is on a conveying path of the bags, the circular track being substantially parallel to a conveying direction of the bags and within a plane that runs along longitudinal direction of the bags, and
a time required for the nozzle to complete one revolution is set at an integral multiple of a time required for one bag to be conveyed over a distance between bags.
Needless to say, it is preferable that the speed of the nozzle in the conveying direction of the bags (i.e., the velocity component in the conveying direction) be set so that this speed is substantially the same as the conveying speed of the bags while the nozzle is inserted in the mouth of the corresponding bag. This can be realized in an ideal form by, for instance, setting the speed of the nozzle on the circular track at a speed that is constant and that is substantially the same as the conveying speed of the bags. The direction of revolution of the nozzle must be a direction that is the same as the conveying direction of the bags.
In the above structure, the nozzle is attached to a rotation transmitting member that performs a translational motion with the same radius of revolution and in the same direction of revolution as the nozzle.
The rotation transmitting member that performs this translational motion consistently faces in the same direction. Accordingly, the discharge opening of the nozzle also consistently faces in the same direction (toward the bottom of the corresponding bag) during the revolution of the nozzle. Of course, the revolution of the nozzle is also a translational motion. The mechanism that causes the rotation transmitting member to perform the translational motion includes two rotating shafts and supporting shafts. The rotating shafts rotate in synchronization in the same direction and respective supporting shafts that are attached to the rotating shafts. The supporting shafts are provided so as to be in eccentric positions which are offset by equal distances in the same direction with respect to the rotating shafts and revolve about the rotating shafts by the rotation of the rotating shafts. The rotation transmitting member is connected to these supporting shafts and makes a translational motion.
It is also preferable to install a plurality of nozzles on the rotation transmitting member so that the nozzles are arranged in the same direction as the conveying direction of the bags at intervals that are the same as the distance between bags that are next to each other. When only a single nozzle is installed along the conveying path of the bags, the time required for the nozzle to complete one revolution is set to be equal to the time that is required for one bag to be conveyed over the distance between bags. To the contrary, when a plurality of nozzles are employed, the time required for each nozzle to complete one revolution is set at a time that is obtained by multiplying the time required for one bag to be conveyed over the distance between bags next to each other by the number of nozzles. In this case, the radius of revolution of the nozzles is increased by the same factor.
The opening apparatus of the present invention is used mainly for bags that are conveyed horizontally in the direction of width of the bags with the bags being held in a vertical attitude and with the mouths of the bags facing upward, and further with both edges of the bags being held by grippers so that the bags are suspended or with the bags being held by retainers, etc. However, the opening apparatus of the present invention is also used in cases where the bags are conveyed horizontally in a direction other than the direction of width (e.g., in the direction perpendicular to the direction of width). In either case, the nozzle(s) revolve continuously on circular track(s) in a vertical plane that is parallel to the conveying direction of the bags (the he longitudinal direction of the bags is the vertical direction). In addition, the opening apparatus may take a structure in which bags are conveyed in the lateral direction, e.g., in which the bags are set in a horizontal attitude and conveyed in the direction of width and in the vertical direction.
Furthermore, the opening apparatus of the present invention is used mainly in cases where bags are conveyed in a rectilinear manner. However, by way of utilizing the flexibility of the bags, the opening apparatus can be used in cases where bags are conveyed along a curved conveying path as long as the curvature is relatively small. This structure refers to a case in which, for instance, the bags are held by numerous grippers disposed on the circumference of a rotating table that rotates in the horizontal direction, so that the bags are conveyed along a circular track with a relatively large radius in a vertical attitude with the mouths of the bags facing upward. In such cases, the circular track for the nozzle may be set by using, for instance, the mean conveying direction of the bags in a zone in which the nozzle is inserted into the bag as a reference. In concrete terms, this track for the nozzle is located within a vertical plane parallel to a tangent drawn to the conveying path of the bags at the position of maximum lowering of the nozzle. Alternatively, if a plurality of nozzles are installed in the above configuration, then the tracks may be set using the mean conveying direction for the same number of bags that correspond to the plurality of nozzles.
Furthermore, when bags are conveyed in the direction of width thereof with the bags being suspended in a vertical attitude, a pair of guide members can be employed. Typically, the guide members are respectively provided on either side of the conveying path of the bags so as to face the vicinity of the bottoms of the bags. The guide members approach and move away from the bags in relative terms. In other words, the guide members approach the bag surfaces in the vicinity of the bottoms of the bags from both sides prior to the initiation of the blowing-in of a gas from the nozzles, thus correcting warping of the bags; and then the guide members are moved away immediately after the blowing-in of the gas is initiated.